There's a couple things I want to improve on before I repaint the truck I'm working on.

First is the box. The back wall wasn't exactly flat where it meets the bed. Note the "step" on the right and how it thickens out on the left.
So I filed it flat. This box is actually from a second kit but it's denticle to the first.

The other issue is while this box, from one of the '84 GMCs mates up well to the newer cabs, it's a touch wide at the top and narrow at the bottom when up against the older '78 cab.
While I did file it a bit at the top edges before I painted it the first time, it's still off a bit.

So a quick cut down the inside corner on both sides will remedy that. I cut down about 1/2 way with a regular X-acto saw blade, pulled the top so the cuts closed and glued them with lacquer thinner.

This way it not only brought the top of the box in flush with cab but also spread the bottom slightly so it now also matches.

That was the first mod I wanted to make before the re-paint. There's another mod and a couple additions I want to do so me screwing up the first paintjob will have a silver lining.